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A metric for quantifying reverse osmosis membrane performance

Inspired by the thinking of Randy Truby and Jim Birkett to find a single figure of merit for seawater RO membranes, I thought I’d see if I could compare the performance of a selection of membranes currently on the market.

To begin I plotted the nominal flux and rejection of 8” membranes from Toray, Filmtec, Hydranautics and NanoH2O – note the membranes that compete directly (e.g. at 99.8% rejection and a flux of about 38 lmhb). The problem I have with data in this form is that neither flux nor rejection are properties of the membranes. Furthermore, rejection depends upon flux – with higher fluxes tending to increase the relative amount of water passing compared to salts and thus increasing rejection. Therefore, I took the data from Fig. 1 and computed the water permeability and salt permeation coefficient for each membrane*. I then took this data and generated Fig. 2.

Fig. 2 has a number of remarkable points:

We typically regard both membrane permeability and the salt permeation coefficient to scale linearly with the thickness of the active layer (the solution diffusion model). For this reason, any straight line drawn from the origin represents a membrane with the same active layer chemical composition but of decreasing thickness as one moves away from the origin.
Following the above logic, the three Hydranautics membranes appear to have similar active layer chemistry but different thicknesses. The Toray membranes seem to include membranes of two different chemical compositions, as do the NanoH2O membranes.
Hydranautics, Toray and NanoH2O membranes show the expected trade-off between water permeability and salt permeation coefficient. An improvement in one leads to a dis-improvement in the other. By contrast, the Filmtec membranes do not illustrate this trend. This is surprising and begs the […]

Eldridge and Dykema: Water is worth an investment

Having had the pleasure to participate in the Massachusetts Water Innovation Mission to Israel with Senator Dykema and Representative Eldridge last December, I wanted to share an encouraging shared op-ed by about the importance of water investment in Massachusetts.
Water is worth an investment
Every day, without thinking twice, we wash our faces and brush our teeth with safe, clean water. Water plays a fundamental role in our everyday lives, yet we often fail to appreciate the systems that bring it to our tap every day. The Globe’s week-long series highlighting the importance of water infrastructure calls attention to this critical yet often ignored issue in Massachusetts. It’s time that we start paying attention.

Largely unseen to us, our cities and towns maintain over 125,000 miles of sewer pipes and 100 municipal wastewater treatment plants, in addition to thousands of drinking water wells and over 200 surface water supplies. According to recent findings of the state Water Infrastructure Finance Commission (WIFC) we co-chaired, the state is failing to adequately invest in maintaining these systems. The commission estimated a $10.2 billion gap in drinking water and $11.2 billion gap in wastewater funding over the next 20 years. This gap will only grow the longer we wait to address it.

According to the EPA, water main breaks are occurring every 2 minutes across the country, and Massachusetts is no exception. Federal funding for water infrastructure was once a primary source of water infrastructure funding, but has decreased dramatically. At the same time we’re also faced with an increased need to more comprehensively address water contaminants ranging from organics like phosphorus to remnants like pharmaceuticals.

Here in Massachusetts, we’ve taken the first steps toward addressing this problem by working with interested stakeholders, […]

Welcome to the MIT Water Club blog

Welcome to the MIT Water Club website. We are proud to announce the launch of our new blog platform, which will allow water researchers, enthusiasts and professionals to tap into the thinking of leading MIT affiliates in the water field. In upcoming weeks, selected MIT Water Club experts and guest contributors will begin sharing their insights on this webpage, so stay tuned for updates!

We’d like to thank the Avada WordPress theme, Brentan Alexander and the energyfolks team for their help in setting up this website.